The Diffusive Role of Turbulence in an Intense Tropical Cyclone

Using a large eddy simulation, we investigate the role of turbulent eddies in the inner core of a Category 5 tropical cyclone. We find that turbulent momentum diffusion significantly influences the mean wind field: acting to weaken the maximum tangential velocity, diminish the strength of radial inflow into the eye, and suppress the magnitude of the mean eyewall updraft.

Both vertical and radial turbulent eddy tendencies are shown to affect the TC mean wind field, with the former being dominant in most of the inflowing boundary layer and the eyewall, while the latter becomes comparatively significant only in the eyewall. In this sense, the inflowing boundary layer of a TC is analogous to traditional atmospheric boundary layers, much unlike the inner eyewall region. Additionally, the Louis-type asymptotic formulation of vertical mixing length is shown to be less accurate as the eyewall is approached.

Finally, the down-gradient eddy viscosity hypothesis is evaluated and shown to be a reasonable approximation for most of the HBL, except in certain weak-gradient zones in the eyewall and slightly inwards of the eye-eyewall interface.